Ignition coils are fundamental components in gasoline-powered vehicles, playing a crucial role in starting and running the engine. While modern automotive technology has advanced significantly, the core principle of how a car coil works remains rooted in technology developed over a century ago. Understanding this principle is key to grasping the basics of automotive ignition systems.
A Brief History of Ignition Coils
The origins of the ignition coil can be traced back to the early 20th century and the ingenuity of American inventor Charles Kettering. Around 1910-1911, Kettering developed a groundbreaking coil ignition system for a major car manufacturer. His innovation was the first electrical system capable of powering both the starter motor and the ignition system simultaneously. This system, utilizing a battery, generator, and a more comprehensive electrical setup, provided a consistent electrical supply to the ignition coil, marking a significant step forward in automotive technology.
Figure 1: Diagram illustrating the primary components of a classic Kettering ignition system, showcasing its mechanical distributor and single coil design.
The Kettering system, as illustrated in Figure 1, employed a single ignition coil to generate a high voltage. This voltage was then directed to a rotor arm within the distributor assembly. The rotor arm, acting as a rotating switch, sequentially pointed the high voltage to a series of electrical contacts – one for each engine cylinder. These contacts were connected via spark plug wires to the spark plugs, ensuring that the high voltage was delivered to the correct cylinder in the engine’s firing order.
The Kettering ignition system became the dominant ignition technology for mass-produced gasoline vehicles for decades. It remained virtually unchallenged until the 1970s and 1980s, when electronically switched and controlled ignition systems began to supersede these mechanical systems, paving the way for more efficient and reliable ignition technology.
The Fundamental Principle: Electromagnetism in Car Coils
To comprehend how a car coil works, it’s essential to understand the basic physics principles at play: electromagnetism. Ignition coils leverage the intrinsic relationship between electricity and magnetism to generate the extremely high voltages needed to create a spark at the spark plugs.
When an electric current flows through a conductive wire, such as the windings within an ignition coil, it generates a magnetic field around the coil. This magnetic field, more accurately termed magnetic flux, essentially stores energy that can be converted back into electrical energy when needed.
Figure 2: Visual representation of electric current flowing through a wire coil, demonstrating the creation of a surrounding magnetic field and energy storage.
As depicted in Figure 2, when the electric current is initially switched on, the current flow rapidly increases to its maximum level. Concurrently, the magnetic field expands and strengthens until it reaches its maximum capacity and stabilizes, coinciding with the stabilization of the electric current. Conversely, when the electric current is switched off, the magnetic field collapses back towards the coil of wire, releasing the stored energy.
The strength of this magnetic field is influenced by two primary factors:
- Current Strength: Increasing the electrical current applied to the coil wire directly strengthens the magnetic field.
- Number of Windings: A coil with a higher number of wire windings will generate a stronger magnetic field for the same current.
Inducing Voltage with a Changing Magnetic Field
A crucial aspect of how a car coil works is the principle of electromagnetic induction. If a coil of wire is exposed to a magnetic field, and that magnetic field changes or moves relative to the coil, it induces an electric current within the coil. This phenomenon is known as ‘inductance’.
This effect can be easily demonstrated by moving a permanent magnet near a coil of wire. The motion of the magnet, causing a change in the magnetic field around the coil, induces an electric current in the wire.
Figure 3: Illustration showing a permanent magnet moving near a coil of wire, visually demonstrating the induction of electric current due to the changing magnetic field.
The magnitude of the voltage induced in the coil is primarily determined by two factors:
- Rate of Change of Magnetic Field: The faster the magnetic field changes (or the speed of movement of the magnet) and the greater the change in the magnetic field’s strength, the higher the induced voltage.
- Number of Windings: Increasing the number of windings in the coil directly increases the induced voltage.
The Role of a Collapsing Magnetic Field in Ignition Coils
In the context of ignition coils, it’s the collapsing magnetic field that is harnessed to generate the high voltage spark. When an electric current is used to create a magnetic field in the coil, any change in this current (whether an increase or decrease) results in a corresponding change in the magnetic field. Critically, when the electric current is switched off abruptly, the magnetic field rapidly collapses. This collapsing magnetic field induces an electric current into the coil itself.
Figure 4: Diagram depicting the rapid collapse of a magnetic field when the electric current is switched off, illustrating the induction of another electric current within the coil.
Similar to how a faster movement of a magnet increases induced voltage, a more rapid collapse of the magnetic field will induce a higher voltage within the coil. Furthermore, increasing the number of windings in the coil will also contribute to a higher induced voltage during the magnetic field’s collapse. This principle is crucial for generating the tens of thousands of volts needed for spark plug ignition.
Mutual Inductance and Voltage Transformation in Car Coils
Ignition coils utilize a principle called ‘mutual inductance’ to amplify voltage. This involves two coils of wire placed in close proximity – the primary winding and the secondary winding. When an electric current flows through the primary winding, it creates a magnetic field that encompasses both the primary and the secondary windings.
Figure 5: Diagram illustrating mutual inductance, showing the magnetic field from the primary winding extending to and surrounding the secondary winding, enabling voltage transformation.
As shown in Figure 5, when the electric current to the primary winding is switched off and the magnetic field collapses, it induces a voltage in both the primary and the secondary windings. This interaction is mutual inductance.
For ignition coils, and indeed for many types of electrical transformers, a crucial design feature is that the secondary winding is constructed with significantly more windings than the primary winding. Consequently, when the magnetic field collapses, a much higher voltage is induced in the secondary winding compared to the primary winding. This is the transformer action at the heart of how a car coil works.
Figure 6: Comparison of primary and secondary windings, highlighting the greater number of windings in the secondary coil and its role in inducing a higher voltage during magnetic field collapse.
Figure 6 visually represents this difference in windings. A typical ignition coil might have a primary winding with 150 to 300 turns of wire, while the secondary winding can have 15,000 to 30,000 turns – approximately 100 times more.
Initially, the car’s electrical system applies around 12 volts to the primary winding of the ignition coil, creating the magnetic field. When a spark is required at a spark plug, the ignition system interrupts the current flow to the primary winding. This causes the magnetic field to collapse rapidly. The collapsing magnetic field induces a voltage in the primary winding, typically around 200 volts. However, due to the winding ratio, the voltage induced in the secondary winding is amplified approximately 100 times, reaching around 20,000 volts or more.
This process of using mutual inductance and a high winding ratio to transform a low voltage (12V) into a very high voltage (20,000V+) is the ‘transformer action’. In an ignition coil, the primary and secondary windings are wrapped around an iron core. This iron core significantly enhances the strength and concentration of the magnetic field and flux, thereby making the ignition coil much more efficient in voltage transformation.
In summary, a car coil works by using electromagnetic induction and mutual inductance to transform a low voltage from the car’s battery into the high voltage needed to create a spark at the spark plugs, initiating combustion and powering the engine. This ingenious application of physics principles remains fundamental to automotive ignition systems even in today’s advanced vehicles.
